1. Field of the Invention
The present invention relates to an electric motor.
2. Description of the Related Art
Motors including a bearing mechanism using fluid dynamic pressure are known and have often been used in storage disk drives. An example of a dynamic pressure fluid bearing apparatus in a spindle motor is disclosed in JP-A 2007-162759 and includes a shaft body and a tubular sleeve body inside which the shaft body is inserted. The shaft body is fixed to a base plate of the motor. The sleeve body is fixed to a rotor of the motor. The shaft body is provided with a first and a second thrust flange. The first and second thrust flanges are both annular and are arranged on an upper and a lower side of the sleeve body, respectively. In the dynamic pressure fluid bearing apparatus, a radial bearing portion is defined between the shaft body and the sleeve body, and a thrust bearing portion is defined between each of the two thrust flanges and the sleeve body. In addition, the sleeve body includes communicating holes defined therein to provide communication between two thrust gaps. Tapered seal portions are defined in the vicinity of upper and lower end openings of the communicating holes.
Another example of a fluid dynamic bearing motor which is disclosed in U.S. Pat. No. 6,991,376 includes a shaft, a top plate, a bottom plate, and a hub. The top plate and the bottom plate are fixed to an upper end and a lower end of the shaft, respectively. The hub is arranged between the top plate and the bottom plate, and is supported so as to be rotatable with respect to the shaft. The hub includes a recirculation channel extending therethrough defined therein. An upper portion of the hub includes a projecting portion arranged radially outward of an outer edge portion of the top plate. A capillary seal is defined between the projecting portion and the outer edge portion of the top plate. A lower portion of the hub includes another projecting portion arranged radially outward of an outer edge portion of the bottom plate. A capillary seal is also defined between the other projecting portion and the outer edge portion of the bottom plate. Influence of a pressure gradient of a lubricating oil in each of the capillary seals is minimized by the recirculation channel being arranged radially inward of the capillary seals.